No wonder I thought there must be a secret retaining clip for these drums. I've never seen drums so worn out and with such a pronounced ridge. We bought the van with about 190,000 miles on it and it's generally in great shape, but I guess the prior owners weren't interested in the rear brakes. Just inside the 1/8" ridge is a little groove just about as deep as the ridge is tall. I never thought I'd have to roll the adjuster screw in that far. All I can say is WOW. I'll be picking up two new drums after work today...